ASD Beam Design Bending – – lateral stability – unbalanced combination of laminations (gluelam) Shear – Deflection – Bearing (for a rectangular beam)

Lateral Stability Cause Result – lateral instability – decrease in allowable stress compression Consider this effect by C L * C L is a similar adjustment factor with C P * C P will be discussed in Ch. 7 (for column)

Lateral Stability full lateral support – appropriate connection of a roof or diaphragm (sheathing) – l u = 0 Approximate method – depth-to-thickness ratio (d/b) = 6 bridging or solid blocking required at intervals of 8 ft max. b d

Lateral Stability Solid blockingBridging

Lateral Stability (using C L ) Concept (Euler Buckling) – Euler critical buckling stress – Euler-based critical buckling stress K bE = for visually graded lumber = for MEL (machine evaluated lumber) = for MSR (machine stress rating) or gluelam

Lateral Stability (using C L ) Procedure of computing C L Evaluating l u Evaluating l e Calculating R B Calculating F bE Calculating C L unbraced length of beam slenderness ratio b d

Lateral Stability (using C L ) Effective unbraced length, l e

Lateral Stability (using C L ) Calculate C L - F bx * = tabulated bending stress for x axis multiplied by adjustment factors (except C fu, C V, and C L ) - E y ’ = modulus of elasticity about y axis multiplied by adjustment factors

Lateral Stability (Example) w TL = 1k / ft, D+S 48’ 6.75* F-1.8E gluelam psi

Lateral Stability (Example) * Note Allowable Bending Stress for Strong Axis: Choose the smaller

Bearing Stress vs.

Unbalanced Combinations of Laminations